"Overall, women exposed to secondhand smoke have up to a 90% greater risk
of breast cancer, the report says."

Although recent studies have linked smoking to breast cancer, no major public
health group, including the American Cancer Society, the Centers for Disease
Control and Prevention and the National Cancer Institute, has declared it a cause
of the disease that kills 40,000 women each year in the USA.

The finding by scientists for the Air Resources Board — whose early efforts to
regulate auto emissions were a model for the rest of the country — could fuel
workplace smoking bans in more states. And it is likely to refocus the scientific
debate over the link between smoking and breast cancer.
 (Related story: Firestorm could be brewing)

"I have to say without reservation it will stimulate continued and accelerated
scientific evaluation of the smoking and breast cancer issue," says
Terry Pechacek, associate director for science in the CDC's office on
smoking and health.

A scientific review panel is expected to approve the report as early as
Monday and forward it to the Air Resources Board, which has broad state
authority to regulate air pollution.

The 1,200-page report analyzes new data on the extent of Californians'
exposure to secondhand smoke and more than 1,000 studies of health
effects from secondhand smoke.

The conclusion that secondhand smoke causes breast cancer, particularly
in younger women, challenges conventional scientific thinking because most |
studies, until recently, had found no connection between female smokers
and breast cancer.

But California scientists based their conclusion on recent human studies that
they determined had more careful assessments of long-term exposure to
tobacco smoke. The report also gave more weight to toxicology evidence
from animal studies than previous studies by the surgeon general and others.
It's well-documented that chemicals from cigarettes cause breast cancer
in lab animals.

Overall, women exposed to secondhand smoke have up to a 90% greater
risk of breast cancer, the report says. It says secondhand smoke kills as
many as 73,400 a year in the USA.

The report did not estimate the number of additional new breast cancer
cases annually, and scientists did not calculate risk levels based on doses
of secondhand smoke.

Tobacco companies, in public comments filed with the board, say the
report gives little weight to studies that found no breast cancer connection.

A new surgeon general's report on secondhand smoke is expected this year.

"The topic is still under review," says the report's senior scientific editor,
Jonathan Samet, an epidemiology professor at Johns Hopkins University.

"It's controversial," Samet says. "Concluding that passive smoke causes
breast cancer has potentially powerful implications for tobacco control
and breast cancer control. So there has been tension over it."